1. Field of the Invention
This invention relates to coin validators used in various automatic service devices of a vending machine or the like, and more particularly to such validators which discern the thickness and/or patterns of coins in a non-contact manner.
2. Description of the Related Art
Electronic coin validators used very often today include an oscillator coil disposed on one side of a coin path and a receiver coil disposed on the other side of the coin path and coupled electromagnetically to the oscillator coil to detect the outer shape and material of a coin during its passage to determine the validation and kind of the coin in accordance with an attenuated waveform of a voltage output by the receiver coil.
These validators are suitable for detecting the diameter and material of a coin using the oscillator and receiver coil, but are not suitable for detecting the thickness and pattern of the coins. If these validators detect the thickness and pattern of a coin, a signal containing a component depending on the material of the coin appears in the receiver coil output, so that it is necessary to provide a circuit to eliminate signal components depending on the coin material, and hence the structure of the validator would be complicated. In order to respond to a change in the thickness of its details such as a pattern, the coin must be stopped temporarily, or an extremely high speed circuit unit must be used, so that the mechanism and circuit structure would be complicated. It is impossible to discern a false coin, especially, of the same material and shape as a genuine one using such selective method.
Generally, the face of a false coin is flat while the face of a genuine coin has a rugged pattern and an uneven thickness.
A method of selecting a coin in accordance with a varying electrode capacitance due to a rugged face or appearance of the coin, namely, caused by inserting the coin between a pair of electrode plates, is disclosed, for example, in Japanese Published Examined Patent Application Sho 39-21291.
In the selective method disclosed in the Application, when a coin to be selected is inserted between the pair of electrode plates, the static capacitance present between the pair of electrode plates changes. Such pair of electrode plates are connected as one of the elements of a capacitor bridge or as one of oscillating elements of an oscillator to thereby select a coin using an unbalance in the capacitor bridge or an oscillation or non-oscillation of the oscillator.
However, since the electrode structure includes a mere arrangement of two opposing electrode plates, the electric lines of force from the electrode plates are dispersed, so that a fine change in the rugged face of the coin cannot be detected, and secure detection cannot be achieved.
It is therefore an object of the present invention to provide a coin validator which discerns the thickness and/or pattern of a coin with high reliability.